Posted for Zeeya Merali
With all the hoopla around the LHC’s plans to “recreate the big bang” it is easy to forget that the particle accelerator’s more modest cousin, the Fermilab Tevatron collider, in Batavia, Illinois, is still chugging along and generating new data. But Fermilab has now managed to seize back the headlines, making it into the New York Times with claims that it could have found a “possible explanation for our own existence”. No, physicists haven’t uncovered the meaning of life, but rather, new data is providing a possible clue about why the universe is composed of matter rather than antimatter.
All things being equal, the early universe should have produced the same quantities of matter and antimatter, which would have annihilated, leaving nothing behind to form stars, galaxies and people. So the puzzle has been to explain the bias towards matter. The D0 collaboration at Fermilab think they have found a hint of what the source of this discrepancy might be – a process that favours the production of matter over antimatter.
Their claim revolves around particles known as neutral B-mesons (made up of a “bottom” antiquark paired with either a “down” quark or “strange” quark) and its antiparticle (a “bottom” quark paired with either a “down” antiquark or a “strange” antiquark). Neutral B-mesons and their antiparticles ultimately decay producing, amongst other things, a mix of muon particles (elementary particles that are similar to electrons, but heavier) and antimuon particles.
The twist is that neutral B-mesons spontaneously swap identities, shifting trillions of times a second between their particle and antiparticle alter-egos. If they spend slightly longer in one identity than the other, this will affect the ratio of matter to antimatter produced. The key discovery by D0 is that, indeed, 1% more muons are found than antimuons.
The standard model of physics does allow antiparticles and particles to have subtly different properties in certain cases, and in the past physicists have found examples of other processes that favour matter – but these have not been enough to explain the huge difference in matter and antimatter we see today. By contrast, the D0 results are about 50 times the level that could be explained by the standard model. If the result is confirmed by future experiments, it means that we need new physics to explain what’s going on, either because some unexpected new particle is interfering with the process, or because particles are interacting in a more complicated way than we think.
The results may not ultimately stand up. One possible source of error is that other exotic particles are being mistaken for muons. But tantalizingly the results do fit with reports two years ago that data from D0 and CDF (its sister collaboration at Fermilab) suggest that new physics is needed to explain some related B-meson processes.
If nothing else, it at least proves that Fermilab is not dead yet.
Image: Tevatron / Reidar Hahn – Fermilab Visual Media Services